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添加 'shell/shell变量提取赋值.md'

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iProbe 2023-08-12 16:13:30 +08:00
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|表达式|含义|
|${var:-aa}|若var为空或未设定, 返回aa, var值不变|
|${var:=aa}|若var为空或未设定, 返回aa, var=aa|
|${var:+aa}|若var有值 返回aa, var值不变|
|${var:?aa}|若var为空或未设定 返回aa并退出shell, 若aa无值, 则输出parameter null or not set, 用于检测var是否被正确赋值|
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